Mitochondria are essential to cell survival as the main producers of ATP via oxidative phosphorylation. However, the mitochondria respiratory chain is also a major source of oxidative free radicals. For example, radical production can occur as a result of the reaction of mitochondrial electron carriers, such as ubiquinol, with oxygen to form a superoxide. Superoxides react by dismutation to hydrogen peroxide, which can decompose to hydroxyl radical. In addition, superoxides react with nitric oxide to form peroxynitrite and other reactive oxidants.
Aging is associated not only with increased reactive oxygen species (ROS) production, but also a decrease in the endogenous antioxidant defense mechanisms. Mitochondria are particularly vulnerable to oxidative stress because they are continuously exposed to ROS. As a consequence, mitochondria decay is often associated with aging.
Free radicals, including ROS, and reactive nitrogen species (RNS) produce diverse non-specific damage to biological molecules, including lipids, proteins, RNA and DNA. Such damage of these molecules has been implicated in numerous clinical disorders, such as atherosclerosis, preeclampsia, Alzheimer's disease, Parkinson's disease and arthritis.
Antioxidant therapy can potentially delay the aging process, and be beneficial in a host of human diseases and conditions, such as those described above. However, the development of specific mitochondrial therapies has been hampered by the difficulty of delivering antioxidant molecules to mitochondria in vivo. For example, the molecule must first be taken up across the plasma membrane into the cytoplasm, and then targeted selectively to mitochondria.
None of the currently available antioxidant compounds specifically target mitochondria. The endogenous antioxidants, superoxide dismutase and catalase, are poorly absorbed orally, have short half-lives, and do not cross the blood-brain barrier. The natural antioxidants (e.g., Vitamin E, coenzyme Q, polyphenols) are not water-soluble and tend to accumulate in cell membranes and only cross the blood-brain barrier slowly.
Therefore, there is a need for improved methods of reducing oxidative damage with antioxidative compounds that cross cell membranes. In addition, it would also be beneficial for the antioxidative compounds to specifically target mitochondria.